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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Collections open source project
//
// Copyright (c) 2022 - 2024 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//
struct DictionaryStatistics {
/// The sum of all storage within the hash table that is available for
/// item storage, measured in bytes. This does account for the maximum
/// load factor.
var capacityBytes: Int = 0
/// The number of bytes of storage currently used for storing items.
var itemBytes: Int = 0
/// The number of bytes currently available in storage for storing items.
var freeBytes: Int = 0
/// An estimate of the actual memory occupied by this hash table.
/// This includes not only storage space available for items,
/// but also the memory taken up by the object header and the hash table
/// occupation bitmap.
var grossBytes: Int = 0
/// An estimate of how efficiently this data structure manages memory.
/// This is a value between 0 and 1 -- the ratio between how much space
/// the actual stored data occupies and the overall number of bytes allocated
/// for the entire data structure. (`itemBytes / grossBytes`)
var memoryEfficiency: Double {
guard grossBytes > 0 else { return 1 }
return Double(itemBytes) / Double(grossBytes)
}
}
extension Dictionary {
var statistics: DictionaryStatistics {
// Note: This logic is based on the Dictionary ABI. It may be off by a few
// bytes due to not accounting for padding bytes between storage regions.
// The gross bytes reported also do not include extra memory that was
// allocated by malloc but not actually used for Dictionary storage.
var stats = DictionaryStatistics()
let keyStride = MemoryLayout<Key>.stride
let valueStride = MemoryLayout<Value>.stride
stats.capacityBytes = self.capacity * (keyStride + valueStride)
stats.itemBytes = self.count * (keyStride + valueStride)
stats.freeBytes = stats.capacityBytes - stats.itemBytes
let bucketCount = self.capacity._roundUpToPowerOfTwo()
let bitmapBitcount = (bucketCount + UInt.bitWidth - 1)
let objectHeaderBits = 2 * Int.bitWidth
let ivarBits = 5 * Int.bitWidth + 64
stats.grossBytes = (objectHeaderBits + ivarBits + bitmapBitcount) / 8
stats.grossBytes += bucketCount * keyStride + bucketCount * valueStride
return stats
}
}
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